1. Field of the Invention
The present invention relates to an X-Y table employing linear motors as its drive source.
2. Description of the Prior Art
A typical conventional X-Y table has heretofore been arranged such that a table body mounted on a base through an intermediate saddle can slide in both the X-and Y-axis directions, orthogonal to each other. The feed mechanism of the X-Y table has been constituted by a combination of ball screw and nut assemblies and rotary motors such as a servomotor or stepping motor (see the specification of Japanese patent application laid open to public inspection under No. 214015/1983).
More specifically, a ball screw shaft is rotatably disposed on the upper side of the base so as to extend in an X-axis direction, and a ball nut, which is screwed onto the screw shaft, is secured to the intermediate saddle. A rotary motor is operably connected to one end of the ball screw shaft so that the intermediate saddle is fed in the X-axis direction along the ball screw shaft by the rotation of the motor. Similarly, a ball screw shaft is disposed on the upper side of the intermediate saddle so as to extend in the Y-axis direction perpendicular to the longitudinal axis of the first ball screw shaft, and a ball nut screwed onto the second ball screw shaft is secured to the lower side of the table body. A rotary motor is operably connected to one end of this ball screw shaft so that the table body is fed in the Y-axis direction relative to the intermediate saddle by the rotation of the corresponding motor.
A feed apparatus has also been known in which, when a ball screw shaft is rotated, the associated ball nut is also rotated by a rotary motor relative to the ball screw shaft, thereby allowing the table body to be selectively moved in a large-feed mode in accordance with the sum of the movements of the ball screw shaft and the ball nut or in a fine-feed mode in accordance with the difference therebetween, respectively.
In the last-mentioned conventional X-Y table, however, the feed of the table body in the X- and Y-axis directions is controlled by controlling the rotation of the respective rotary motors, and the table body, which is one of the movable members, is equipped with a motor, a ball screw shaft and the like and therefore has a relatively large inertia, so that the X-Y table has a poor response at the start and end of the feed operation, thus resulting in an unfavorably low degree of accuracy in the positioning of the table body.
The employment of ball screw and nut assemblies involves the disadvantages that a ball screw shaft may be twisted by rotational torque, and that backlash may occur between a ball screw shaft and a ball nut, resulting in a poor response. This also makes it impossible to increase the degree of positioning accuracy.
Furthermore, the above-described prior art commonly requires a relatively large space for mounting of the rotary motors and the ball screw and nut assemblies, resulting in an increase in the overall size of the X-Y table.
Similarly, the prior art arrangement, which enables the X-Y table to be selectively fed in a fine-feed mode and a large-feed mode, needs a motor for rotating each ball nut and another motor for rotating each ball screw shaft, that is, it needs two motors for each of the feed operations in the X- and Y-axis directions. In consequence, the overall weight and hence inertia of the table body increases to reduce the positioning accuracy thereof as well as enlarge the overall size of the X-Y table.